This invention relates to a gear differential utilizing cam grooves to rotate two outputs, and allow relative differences in the speed of rotation of the two outputs under certain conditions.
Gear differentials are utilized in most modern vehicles. A differential receives a single drive input, and then splits that drive input between two outputs. As an example, gear differentials are utilized on most drive axles to split rotation between the two opposed wheels.
In a typical differential, a gear case surrounds the output shafts. The gear case has a gear which is driven by a drive input to rotate the case. Pinion gears rotate with the case, and engage and drive gears associated with each of the output shafts. This arrangement allows the two output shafts to rotate at differential speeds.
While standard gear differentials are widely utilized, they do require close machining tolerances, and specialized equipment to produce the required gears economically.
Moreover, under certain conditions it is desirable to not allow relative rotation between the two shafts. As an example, while some limited relative rotation may be desirable such as when the vehicle is turning, excessive differential rotation could be indicative of a slipping wheel. As an example, a wheel slipping on ice, will typically rotate at a higher speed than a wheel which is still engaged on the ground. In such situations, it would be desirable to limit relative rotation. Prior art gear differentials have not always been as successful as desired in limiting this relative rotation.
In the disclosed embodiment of this invention, a cam arrangement is associated with each of the output shafts. The two cams are connected by a first moving member having pins engaged in cam grooves in the cams. When the two output shafts are rotating at the same speed, then the moving member and its pins drive the cams associated with each output shaft at generally equal speeds. However, should the two shafts begin to rotate at different speeds, then the pins will move within the grooves, while still transmitting rotation to the cams. As the pins move within the grooves, the moving member moves axially. As the amount of relative rotation increases, the speed of the moving member also increases.
The moving member is structured such that when its speed increases, there is resistance to further increase in movement. As this resistance increases, the moving member is unable to move freely at increased speed. The moving member thus constrains the two shafts to rotate at a more equal speed.
In preferred embodiments of this invention, the moving member has a pin engaged in a slot in an inner periphery of a differential case. This pin causes the moving member to rotate with the case, but allows the moving member to move axially within the case.
Further, a second moving member is guided in a second set of cam grooves in each of the two cams associated with the shafts. The second set of grooves and the pins associated with the second moving member are offset relative to the first set. In this way, the second moving member will continue to move in a particular direction when the first moving member reaches the extremes of its cam grooves. Thus, there will be no hesitation to continued rotation of the shafts at an end of travel position in the first set of cam grooves.
The second moving member includes a pin received in an axial groove in the inner periphery of the first moving member. Thus, the first moving member and the second moving member rotate together. The pins received in the second set of grooves in the two cams from the second moving member cause the cams to rotate with the second moving member, and hence, the first moving member.
In a preferred embodiment of this invention, the resistance to movement of the first moving member is created by having a passage extend through the first moving member to interconnect fluid chambers at each end of the first moving member. Hydraulic fluid is preferably received in those chambers. As the first moving member moves, fluid moves through the passage. Valves are positioned in the passage and serve to restrict the passage as the speed of the first moving member increases. This resistance to further flow of the hydraulic fluid will result in resistance to increased speed of movement of the first moving member. As movement of the first moving member is restricted, it will drive the slower moving cam, such that the two cams are driven at a more equal speed.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.